1. Field of the Invention
The present invention relates generally to integrated circuit devices, and, more particularly, to baluns and transformers manufactured on integrated circuit chips.
2. Description of Related Art
Increasingly, due to reliability, performance and cost considerations, devices that previously resided on a printed circuit board (PCB) are being integrated into an integrated circuit (IC) chip. Transformers, inductors, and baluns are examples of devices that have migrated to the IC chip.
Due to the relatively noisy environment on an IC chip, many signals on a chip are typically differential or double-ended signals. Differential signals offer good common-mode rejection of noise; noise typically affects both halves of the differential signal in the same manner, and since information is contained in the difference of both signal halves, the difference does not change appreciably despite the noise that has been added to both halves.
A balun is an example of a device that accepts a single-ended signal and transforms it into a differential signal and vice versa. The term balun suggests its function: conversion of balanced (differential) signals to unbalanced (single-ended) signals. Signals on PCBs are typically single-ended signals. Since IC chips use differential signals, baluns have been placed on PCBs to transform a single-ended signal into a differential signal. Baluns have also been placed on IC chips. However, present designs suffer from asymmetrical parasitic characteristics (e.g., asymmetric parasitic capacitances and resistances) and poor magnetic coupling. The asymmetrical parasitic characteristics cause a differential signal to be asymmetrical. Symmetry in a differential signal is very important to the proper functioning of many differential circuits. Furthermore, poor magnetic coupling results in inefficient energy transfer.
A transformer is another example of a device that has on-chip uses. For example, a transformer can be used to match impedances between amplifier stages while providing DC isolation between the stages. A transformer for differential signals also needs to offer good magnetic coupling as well as symmetrical parasitic characteristics. Present designs do not offer relatively good parasitic characteristics and good magnetic coupling.
Thus, there is a need for baluns and transformers that provide improved symmetry and magnetic coupling.
A method for producing an on-chip signal transforming device is described. The method includes providing a substrate and laying a first conductive layer above the substrate, wherein the first conductive layer has a plurality of interleaved inductors. The method then includes laying a second conductive layer above the substrate, wherein the second conductive layer has at least one inductor.